Traveling concrete extrusion machines are typically used for the making hollow core concrete slabs. These machines have a hopper which receives premixed concrete. The concrete falls into a feed chamber which is mounted on a frame. The machines also have a molding chamber where the concrete is molded into the profile of the slab. One or more spiral conveyors push the concrete from the feed chamber towards the molding chamber and, at the same time, propel the machine in the opposite direction. Each of the spiral conveyors is rotatable about a non-rotating mandrel shaft. A series of mandrels with internal vibrators are connected to the shaft. Similar machines are disclosed, for example, in my earlier U.S. Pat. No. 4,330,242.
The compression on the concrete in the molding chamber is increased where the spiral conveyors have tapered sections such that the flights of each conveyor are larger in diameter towards the molding chamber compared with flights closer to the feed chamber. This arrangement is shown, for example, in my British Patent No. 1,342,601. However, wear is accentuated at the end of the spiral conveyor adjacent to the mandrels. This leads to a rounding off of the conveyor flights in this location and a corresponding reduction in the compression effect otherwise achieved by such a tapered spiral conveyor.
Replacing the spiral conveyors is an expensive proposition since they are made of a special high chromium iron alloy. Moreover this involves dismantling the extrusion machine with attendant high labor costs and loss of production. Accordingly, attempts have been made to provide replaceable sections on the spiral conveyors where wear is most extreme. Such an arrangement is shown, for example, in Canadian patent 1,205,985 to Kiss. This patent shows a conveyor with a replaceable section made in two halves. These halves are connected to the main portion of the main auger by bolts.
However, these bolts are often shaken lose by vibrators in the mandrel. The lose bolts allow halves of the conveyor to disconnect and can cause damage to the machine. Alternatively, the vibrations of the mandrels can cause the bolts to become welded to the main auger. Thus the bolts break off when attempts are made to loosen them to replace the sections of the spiral conveyors.
It is an object of the invention to provide an improved spiral conveyor for a concrete extrusion machine which has a tapered profile, but significantly reduces the wear which is normally concentrated at the end of the conveyor adjacent the mandrels.
It is also an object of the invention to provide an improved spiral conveyor for a concrete extrusion machine which has a replaceable section in a high wear location, but is not adversely affected by vibrations in the mandrel or other parts of the machine since it is not connected to the main auger by bolts or the like.
It is hot still further object of the invention to provide an improved spiral conveyor with a replaceable section which can be easily removed and replaced with a new section without undue labor costs or loss of production of the machine.